Patrick Forterre

Last revision on 02/10/97

My first research interest was in DNA replication at
the exciting time (early seventies) when biochemists were looking for
the true replicase in Escherichia coli and discovered new
unexpected functions involved in DNA metabolism. I fell in love with
DNA gyrase, a fascinating enzyme that produces DNA superhelices, and
proposed a model explaining the action of this enzyme via a
double-stranded DNA break. Half of the model (rotation of the enzyme
on itself) turned out to be wrong, but it was a lot of fun.

In 1982, reading the review papers on Archaebacteria (now renamed
Archaea) by Carl Woese in Scientific American, I decided to work on
enzymes that manipulate DNA superhelices (called DNA topoisomerases)
in these unique microbes, the third form of life on earth. The
original question was : do Archaea possess a gyrase activity, as
classical bacteria, or an enzyme which can only eliminate
superhelices (relaxing enzyme), like all eucaryotic organisms
(including ourselves) ? It turned out that hyperthermophilic archaea
actually contained a reverse gyrase, i.e. an enzyme which produces
superhelices (called positive) winding in the opposite direction from
those (negative) produced by classical gyrase. Positive superhelices
have an increasing number of topological links between the two DNA
strands, and this might counteract the effect of temperature
increasing on DNA structure, such as partial separation (unwinding)
of the two strands or change in the helix path (but this has yet to
be definitely proven).

From that time (1984), I have been working on reverse gyrase in
collaboration with Michel Duguet. In 1986, we discovered that the DNA
of a virus from a hyperthermophilic archaea indeed exhibits a
positive superhelix. Later on, we shown that reverse gyrase is
present in all hyperthermophiles, either Archaea or Bacteria. More
recently, we have shown that reverse gyrase is formed by the fusion
of two proteins: an energy consuming enzyme (ATPase) that ressembles
helicases (enzymes which separate the two strands of the DNA helix)
and a DNA relaxing enzyme. In my opinion, the composite origin of
reverse gyrase and its extreme sophistication argue against the
primitivness of hyperthermophilic microbes.

My initial work on Archaea was made possible by encouragments and
biological material provided by Wolfram Zillig. His invitation at the
second archaebacterial meeting held in Munich in 1985 was a decisive
step in my scientific career. The same year, I joined the laboratory
of Anne-Marie De Recondo in Villejuif to lead a small research group
working on Archaea. She provided me with the unique opportunity to
work freely on my own ideas and to finally defend my "Thèse
d'état" in a favorable context. My former student Christiane
Elie was on my side from the beginning of this adventure. We
discovered the inhibition of archaeal DNA replication by the
eucaryotic inhibitor aphidicolin and later on, in Villejuif, she
purified and characterized two DNA polymerases from thermoacidophilic
archaea, while another pHD student, Mouldy Sioud, discovered that
Archaea are sensitive to antitumoral drugs active against human DNA
topoisomerases.

In 1988, I was invited by Andre Berkaloff to set up my own
laboratory at the Institut of Microbiology in Orsay (south of Paris).
We pursued our work on DNA gyrases and relaxing enzymes (all of them
called DNA topoisomerases) and on DNA polymerases, while extending
our investigations on various aspects of DNA metabolism in both
hyperthermophilic bacteria and Archaea. A former PhD student, Franck
Charbonnier, and a post doc, Purificacion Lopez-Garcia analyzed DNA
from hyperthermophilic archaea and showned that not only viral DNA
but also cellular DNA have higher number of links between the two
strands, compared to organisms living at "normal" temperatures. I
have been involved myself in a study performed by Evelyne
Marguet on the effects of very high temperatures on the DNA
molecule.

A spectacular and recent achievement of our work on DNA
topoisomerases was the discovery by Agnes
Bergerat and Danielle Gadelle of a completely new family of these
enzymes in Archaea, leading to the identification of the protein
which initiates the first step of meiotic recombination in eucaryotes
(breakage of one of the two parental chromosomes).

Our installation in Orsay also allows us to initiate new research
projects. In particular, we also started to work on anaerobes.
Yvan Zivanovic established the
culture conditions for Pyrococcus and related species and
initiated a research project towards the construction of genetic
tools for these microbes (in the frame of a EC Biotech program). This
work was boosted by our collaboraton with Daniel
Prieur via the GDR Bactocean
(Groupement De Recherche CNRS/IFREMER) that led to the identification
and characterization of the first plasmid from hyperthermophilic
archaea. We also help the IFREMER
group working on hyperthermophiles in Brest to start a research
project on the characterization of new hyperthermophilic DNA
polymerases.

In recent years too, Bernard Labedan set up in our lab a research
group on molecular phylogeny and protein evolution. He became our
advisor in tree construction and initiated his own work programm on
bacterial genome evolution.

In February 1996, we organized the first francophone meeting on
the molecular biology of thermophiles at Gif sur Yvette, in the South
of Paris. More than 80 scientists attended the meeting, a strong
indication that this field of research is expending in the
francophone community.

Personnally, I have been more and more involved in intense debates
about the hot origin of life hypothesis and rooting of the tree of
life. Thanks to André Brack and André Adoutte, I got in
touch with the scientific community working on the origin of life and
molecular evolution, respectively. I have tried to challenge some of
the new dogma in these fields, not yet with great success. In 1996, I
co-organized the first meeting on the last common ancestor and beyond
(thanks to the Fondation des Treilles) with the aim to boost
researches in this particular area.